If Facebook wants to maintain its dominance over our social lives online, its acquisition of hot messenger platform WhatsApp indicates it could do so without becoming the hellish, share-everything-with-everyone company from Dave Eggers' "The Circle."

With WhatsApp, Facebook now offers a significant dark social product — a way for users to share content with small groups of people away from the spotlight of a public social network. While Facebook CEO Mark Zuckerberg used the term "open" eight times in a letter defining the company for its IPO, he's clearly also interested in the growing market for more closed-off forms of communication — from private platforms like WeChat and Kik to very, very private platforms like Whisper and Secret.

Our mission is to make the world more open and connected. We do this by building services that help people share any type of content with any group of people they want. WhatsApp will help us do this by continuing to develop a service that people around the world love to use every day.

So what's the impact for publishers? Liz Gannes of Re/code reported Thursday that BuzzFeed has included an option to share content via WhatsApp in iOS — and the WhatsApp button has drawn more action than the Twitter button:

“Every time we looked at WhatsApp’s numbers, it blew us away,” said BuzzFeed president Jon Steinberg. “We knew last April this was a huge social network and have become increasingly obsessed with it.”

BuzzFeed's option to share via WhatsApp is offered alongside icons for sharing via Facebook and Twitter. But as Gannes notes, it's distinct from those platforms in that the sharing is private (i.e. person-to-person), more like SMS texting or email. (Nieman Lab's Joshua Benton helpfully cautions against reading too much into the behavior BuzzFeed observed.)

So what's most interesting about the deal is not that Facebook gobbled up a burgeoning social-media competitor, but that it acquired a platform that allows users to share very differently than Facebook users. Facebook users broadcast content widely; WhatsApp users target content narrowly. Users of Facebook discover content (especially in its new Paper app); users of WhatsApp receive it.

That doesn't look like two services competing in the same space. That looks like two services that, thanks to their massive user bases, together could meet all our sharing needs — both public and private (especially if WhatsApp maintains its appealing commitment to privacy). The biggest social network could become the biggest player in dark social, too, if more consumers turn away from sharing links via Google products like Gmail and Hangouts and toward sharing links via WhatsApp — and if WhatsApp makes a play for tablet and desktop users, too, becoming a cross-platform version of Apple's iMessage, available everywhere all the time.

The New York Times famously highlights dark social sharing throughout its site with its "Most Emailed" widget. It also publishes lists of the stories most tweeted and shared on Facebook. The lists tend to differ in fascinating ways, reflecting not only the platforms' different user bases but also the different thinking behind the decision to share a link with one person versus the decision to share a link with many people. It would be interesting to see if a "Most Shared via WhatsApp" list more closely resembled email sharing or Facebook sharing — or if it surfaced entirely different content, uniquely suited to a WhatsApp sharing mentality.

If readers — particularly younger ones — continue to see WhatsApp as an easier, more relevant way to share content with small numbers of people than comparatively antiquated email and SMS, publishers would do well to follow BuzzFeed's lead, facilitate WhatsApp sharing and see where it leads.

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Sam Kirkland is Poynter's digital media fellow, focusing on mobile and social media trends. Previously, he worked at the Chicago Sun-Times as a digital editor, where he helped launch digital magazines and ebooks in addition to other web duties.